The present invention relates generally to synchro/resolver systems and deals more particularly with the production of resolver based signals directly from a synchro.
The use of direct drive motors in many servo applications, such as, for example, robotics has increased the need for highly accurate position sensors to provide information representative of the motor shaft position. Previously used sensors, such as Hall-effect sensors, encoders and tachometers provided accuracies of about 1.degree. to 2.degree.. Synchro/resolvers used as position sensors often do not have as high a resolution or accuracy as is often desired in direct drive digital servo positioning systems.
Resolvers generally, due to the limited number of poles, usually 20-30 poles, can provide accuracies of only about +/-30 arc minutes. Additionally, a resolver, because of the quadrature relationship of the stator windings, is constructed using stator and rotor parts that are generally different from a motor with which it is used. Consequently, there is often an additional cost associated with using resolvers having a differently configured stator and rotor from those of the motor.
Synchros can generally provide higher positional accuracies than resolvers and often are constructed using a stator and rotor having the same configuration as the drive motor with which it is used. The synchro however, unlike the resolver which has a signal amplitude at the stator output that varies according to the sine and cosine of the motor shaft angle, has a stator output signal that is 120.degree. out of phase with the other stator output signals. Because resolver-to-digital converters operate from resolver-based signals, i.e. sine and cosine, the synchro stator outputs must be converted or transformed using a Scott-T transformer or electronic circuitry to provide the desired resolver sine-cosine signal relation.
Another drawback using known synchros as position sensors is the requirement of precision and generally expensive components which are necessary to sense the phase current flowing in each stator winding. A voltage drop is developed across a precision current-sensing resistor in series with the phase, and this voltage signal is amplified and converted as explained above or is inputted to a specially made synchro-to-digital converter module which produces a digital synchro position signal as its output. Generally, the magnitude of the voltage signal developed across the current-sensing resistor is very small and requires substantial amplification to be used.
It is a general object therefore of the present invention to provide a synchro position sensor that overcomes the disadvantages generally associated with known synchro position sensors.
It is a further object of the present invention to provide a synchro position sensor that produces resolver-based signals directly from its output, without requiring expensive precision current-sensing resistors or other conversion devices.
It is a yet further object of the present invention to provide a synchro position sensor that is generally less complex to construct, uses less complex circuit components and provides output signals having a relatively large magnitude.